Britain has announced new proposals that could treat asylum seekers who arrive without identity papers as criminals. British officials say most asylum seekers arrive without travel documents, and some even destroy their passports en route to Britain.

Officials say new immigration measures intend to crack down on such abuses and include possible prosecution of asylum seekers who conceal their nationality.

A consultation paper on a new asylum bill was sent to Parliament, and the government expects to introduce the bill next month.

The crackdown is being revealed just three days after the government gave amnesty to the families of 15,000 asylum seekers whose cases had taken years to resolve.

Critics said the amnesty will only attract more asylum seekers who hope they can clog up the system with paperwork and appeals. The issue could become a campaign plank in the general election expected in about 18 months.

A spokesman for the opposition Liberal Democrat party, Mark Oaten, told British radio the government's asylum policy is not consistent and sends mixed signals. "This has all the feel of the Home Office feeling perhaps with the amnesty that they were soft on Friday, so they had to be tough on Monday," he said.

The immigration minister, Beverley Hughes, concedes there are big asylum challenges ahead, but she denied the system has broken down. "It is very difficult for any country to estimate how many people are illegally in the country, because clearly by definition they do not want to be detected, but it is certainly not true to say, at all, that the system is now a shambles," she said.